Refrigeration



21, 1944 P. P. ANDERSON, JR. 2,363,381

REFRIGERATION Filed Aug. 3, 1940 0 07/15? PUMP v v 67 I flVVENTOR/ 2%]. ymgz fi ATToRNEY Patented .Nov. 21, 1944 UNITED STATES PATENT o1=1=1cs A 7 2,363,381 nnrmennsrron 'Philip r. Anderson, In, Evansville, Ind., assignol' to Servel, Inc., New York, N. Y., a corporation of Delaware Application August 3, 1940, Serial No. 35l l,883

5 Claims; (01. 62-119) 7 This invention relates to refrigeration, and is particularly concerned with non-condensible gases that collect in refrigeration systems of the absorption type operated by heat.

. In a low pressure system of this type contain-- ing only a refrigerant and an absorption liquid therefor as the two active fluid components, a

'vm yressureqnihe enerator and condenser is approximately 56 mm. HE

. frigeration system toan extremely low value.

Further, the vacuum pump embodying the invention can be connected either to the condenser or to the absorber of a two-pressure refrigeration system of the type described above, and ordinary variations in temperature of the water oPerat-- ing the aspirator will not greatly affect the operation of the vacuum pump.

Usually the purge valve of a refrigeration systemto which a vacuum pump is connected can only'be opened after the vacuum pump has lowered the pressure in the connection below the pressure existing in the refrigeration system. In

the vacuum pump provided, after the vacuum has been pulled once and theepump left attached to the system, the purge valve may be opened even before operation of the vacuum pump has been started. so that the usual precautionishatmust be taken with respect to keeping Duringperation of the refrigeration system, the purge valve closed until a vacuum has been non-condensible gases may collect in parts thereof to increase the vapor pressure in the system. The collection of non-condensible gases and the resulting increase in vapor pressure in the system is undesirable, because the efliciency of the refrigeration system is reduced and the normal operation thereof may be disturbed.

It is an object of this invention to provide an improvement for removing non-condensible gases from refrigeration systems. I accomplish this by providing, in -a two-pressure system of the type described, an arrangement for utilizing flow of refrigerant from the condenser to the evaporator to effect removal of non-condensible gases from the generator and condenser to the evaporator and absorber; providing a siphon trap in the conduit through which liquid flows from the condenser to the evaporator.

It is another object of the invention to provide an improved vacuum pump for trapping and removing non-condensible gases from a refrigeration system. In the present embodiment the vacuum pump is connected to the absorber although the pump may be connected to other parts of the system, such as, for example, the condenser. The vacuum pump is a two-stage device which possesses inherent advantages' over a single stage pump. A' distinct advantage is also obtained in the vacuum pump provided in that a uniform pressum drop is effected on both sides of a U-tube embodied in the pump when the pump isflrst started. The vacum pump employs an aspirator which is exceptionally fast and can be used to reduce the vapor pressure inthe reproduced by the pump, is avoided. In. addition This is accomplished by taken with respect to keeping the purge valve of the refrigeration system closed until a vacuum has been produced, the vacuum pump provided eliminates a pressure indicating device in the vacuum pump connection to the purge valve of the-system.

The invention, together with the above and other objects and advantages thereof, will be better understood from the following description taken in connection with the accompanying drawing forming a part of this specification, and of which the single figure more or less diagram-y matically illustrates a refrigeration system and a vacuum pump. embodying the invention.

Referring'to the drawing, the present invention is shown in connection with a two-pressure absorption refrigeration system like that described in application Serial No. 239,762 of Albert R. Thomas and P. P. Anderson, Jr., flied November 10, 1938, now Patent No. 2,282,503, granted May 12, 19 2. A system of this type ope erates at low pressures and includes a generator or expeller ill, a condenser ii, an evaporator l2 and an absorber I4 which are interconnected in such a manner that the pressure differential in the system is maintained by liquid columns.

-The disclosure in the aforementioned Thomas and Anderson application may be considered as being incorporated in this application, and, if desired, reference may be made thereto for a detailed description of the refrigeration system. In Fig. 1 the generator It includes an outer shell within which are disposed a plurality of vertical riser tubes l6 having the lower ends thereof communicating with a space H and the upper ends thereof extending into and above the bottom of a vessel IS. The space l9 within shell l5 and about the tubes I6 forms a steam chamber to which steam is supplied through a conduit 20. The space l9 provides for full length heating of riser tubes l6, and a vent 2| is provided at the upper end of shell |5. .A trap conduit 22 is connected to the lower part of shell I5 for draining condensate from space IS.

The system operates at a partial vacuum and contains a water solution of refrigerant in absorption liquid, such as, for example, a water solution of 40% lithium chloride by weight. With steam being supplied from conduit 20 to space l9, heat is applied to tubes |6 whereby water vapor is expelled from solution. The absorption liquid is raised by gas or vapor-lift action with the expelled water vapor forming a central core within an upwardly rising annulus of the liquid. The expelled water vapor rises more rapidly than the liquid and the latter follows the inside walls of tubes I6.

The water vapor flows upwardly through the tubes or risers l6 into vessel l8 which is provided with an apertured baflle 23 and deflectors 24 and 25 at each side of the aperture in the baiiie. The baiile 23 and deflectors 24 and 25 serve as a vapor separator so that expelled water vapor is separated from raised absorption liquid in vessel I8 and flow through conduit 26 into condenser The water vapor is liquefied in condenser H and the water thus formed flows through a U-tube 21 into a flash chamber 28 and then into evaporator l2.

The evaporator l2 includes a plurality of horizontal banks of tubes 29 disposed one above the other and to which are secured heat transfer fins 30 to provide a relatively extemive .heat transfer surface. The end portions of the tubes 29 pass into spaced vertical headers 3|. The water flows from flash chamber 28 through a trap conduit 32 into a liquid distributing trough 33 from which the water flows into the uppermost horizontal bank of tubes 29. The water passes through successively lower banks of tubes through upright open end sections 34'at the ends of tubes 29, whereby shallow pools of liquid are formed in the tubes 29 with excess liquid being discharged from the lower-most bank of tubes 29.

The water supplied to tubes 29 evaporates therein to produce a refrigeration or cooling effect with consequent absorption of heat from the surroundings, as from a stream of air flowing over the exterior surfaces of the tubes 23 and fins 30. The vapor formed in tubes 29 passes out through the distributing trough 33 and open end sections 34 into the headers 3| which are connected at their lower ends to absorber l4. To prevent disturbances in evaporator I! the flash chamber 28 is provided to take care of any vapor flashing of liquid being fed to the evaporator through U-tube 21. The flashed vapor formed in the initial cooling of the liquid flowing from the condenser passes through a conduit 35 into one of the headers 3| and mixes with vapor formed in evaporator II.

In absorber l4 refrigerant vapor is absorbed into concentrated absorption liquid which enters through a conduit 36. The absorption rality of vertically disposed pipe banks 80 which are arranged alongside of each other. Theliquid in the center compartment 0! receptacle 31 is sub-divided and passes into a plurality of smaller end compartments 39 from which liquid flows through conduits 40 into a plurality of liquid holders and distributors ti extending lengthwise of and above the uppermost horizontal pipe sections of pipebanks 33.

Absorption liquid siphons over the walls of the liquid holders 4| with drops of liquid falling Onto and completely wetting'the uppermost pipe sections. Liquid drips from each horizontal pipe section onto the next lower pipesection whereby all of the pipe sections are wetted with at him of liquid.

The water vapor formed in evaporator 52 passes through the headers 3| into the shell of liquid flows from the upper end oi. conduit 36 into a liquid receptacle and distributor 31 in which liquid is distributed laterally of a plu- -|0 and condenser absorber l4 and is absorbed into absorption liquid in the latter. The water vapor absorbed in the liquid dilutes the latter, and the diluted absorption liquid flows through a conduit 32, a first passage in liquid heat exchanger 43, conduit 44, vessel 45, and conduit 46 into the lower space H of generator l0. Water vapor is expelled out of solution in generator ID by heating, and the solution is raised by gas or vapor-lift action in absorber l4 and return from the latter to the generator by force of gravity.

The vessel 45 is cylindrical in shape and disposed about shell |5 of generator I. The heating effect of the steam in space |9 is transmitted through a portion of shell |5 to absorption liquid in vessel 45. In this manner the absorption liquid flowing to generator id through conduit 46 is preheated, as described more fully in Thomas application Serial No.

347,631, flied July 26, 1940. The upper part of vessel 45 is connected by a conduit 48 to vessel l8, so that the pressure in vessel 45 isequalized with the pressure in the upper end of generator The heat liberated with absorption of water vapor in absorber H is, transferred to a cooling medium, such as water, for example, which flows upward through the vertically disposed pipe banks 38. The cooling medium is supplied through a conduit 49 to a horizontal manifold 50 to which the lower ends of the pipe banks 33 are connected. The upper ends of the pipe banks 38 are connected to a manifold 5| to which is connected a conduit 52 through which cooling medium leaves the absorber 4. The conduit 52 is connected to condenser so that the same cooling medium may be utilized to cool absorber l4 and condenser H, with the cooling medium flowing from condenser through conduit 53 to waste.

The system operates at a low pressure with the generator "I and condenser l operating at one pressure and the evaporator |2 and absorber 84 operating at a lower pressure, the pressure diiferential therebetween being maintained by liquid columns. Thus, the liquid column i'ormed in tube 21 maintains the pressure differential beeflected without appreciably restricting flow of liquid.

The liquid column formed in vessel 45 and conduit 45 provides the liquid reaction head for raising liquid in riser tubes 15 by vapor-lift action.

The vessel 45 is of suflicient volume to hold the liquid differential in the system and is of such cross-sectional area that the liquid level therein does not appreciably vary, so that a substantiallyconstant reaction head is provided for lifting liquid in generator l0.

In accordance with this invention, in order to effect removal of non-condensible gases from condenser llv to evaporator l2 and absorber l4, a liquid siphon trap 54 is provided in the U-tube 21. The siphon trap 54 may be of any desired shape, and, as shown, is in the form of a complete circular loop in the down-leg of U-tube 21.

During operation of the refrigeration system, liquid flows from the condenser into loop 54. When the liquid in the right-hand side of loop 54 reaches the level p, the liquid is siphoned from the loop into the down-leg of U-tube 21. The gas in the down-leg of U-tube 21, between loop 54 and the liquid level 2, is trapped by the liquid siphoned from the loop. After the liquid has siphoned from the loop; gas freely passes from the condenser ll through the loop 54 intothe down-leg of U-tube 21. When the liquid from condenser ll again reaches the level 1) in the tube 21.

The gas segregated between the successive short liquid columns or slugs siphoned from loop 54 is compressed by the siphoned liquid and caused to pass through the U-tube 21 by the gravity flow of liquid from condenser to evaporator 12. Thus, when the system is first started and before the pressure difierential has beenbuiltup between the condenser and evaporator, the U-tube 21 completely fills with liquid and gravity flow of liquid is effected from the condenser to the evaporator. Even after the pressure diflerentialhas built up between the evaporator and condenser, and the liquid level is at z, for example, in the down-leg of U-tube 21 due to the higher pressure in condenser ll than in evaporator I2, still flow of liquid is effected by gravity from the condenser to the evaporator. And it is with this gravity flow of liquid and siphoning thereof from loop 54 that eiiects trapping of gas in the down-leg of tube 21 and the transmission of the trapped gas by the liquid to the evaporator. In this way noncondensible gases collecting in the upper part of generator andconde'nser II are eflectively removed from these parts of the system to the evaporator l2 and absorber l4 to which the vacuum pump, embodying another feature of the .invention, is connected for removing non-condensible gases fromthe refrigeration system.

The vacuum pump includes an upper closed vessel 55 which is connected by a'conduit 55 to an aspirator or other suitable pump. An aspirator, in which a suction or vacuum is produced in vessel 55 by connecting the aspirator to a tap supplied with city water at the usual pressures, has been successfully employed. The vessel 55 is provided with a suitable baflle 51 to separate from liquid the gas or vapor which is drawn through conduit 55 by the actionof the aspirator. Into the lower part of vessel 55 extend riser tubes 55 through which a liquid, such as mercury, for example,.is raised from a lower vessel or well 55. The vessel 59 is open at the top and the riser tubes 55 are formed with openings 50 to allow air to enter into the tubes 55, so as to break up the mercury in the extreme lower-parts of the tubes into drops which are raised in the riser tubes 58 due to the vacuum in vessel 55 produced by the operation of the aspir'ator. The tubes 58 extend above the bottom of vessel 55, and the raised mercury flows into the down-leg of U-tube 51, while to the absorber I4 of the refrigeration system.

The non-condensible gases collecting in the evaporator l2, including the gases removed from the generator I0 and condenser ll through U-tube 21 in the manner described above, are heavier than the water vapor formed in evaporator l2.

The water vapor passes from the evaporator I 2 to the absorber 14 at a relatively high velocity. In a refrigeration system having a capacity of live tons, with the system operating at full load and the evaporator at a temperature of about 50 F., the average velocity of the vapor passing from the evaporator to the absorber is about 130 feet per second for the pressure existing in the system.

Under these conditions, the heavier non-condensible gases are swept by natural convection to the farthest point of the path of flow of vapor, which is midway between the headers 3| at the extreme lower part'of the absorber 14-, as described more fully in application Serial No.

350,236, of A. R. Thomas, filed August 3, 1940. In

view of the foregoing.. the conduit 53 terminates in the extreme lower part of the absorber at the middle or central portion thereof.

The mercury flowing from the U-tube 5| into vessel 52 forms slugs at the upper end of a vertical tube 54 connected to the lower part of this vessel. Gas is entrainedbetween the slugs of mercury as they form at the upper end of tube 54. The gas entrained by the mercury slugsis drawn into vessel 52 through conduit 63 which, as pointed out above, terminates in the absorber 14 at the region where the non-con'denslble gases and then passes to the aspirator. The mercury passes from vessel 65 through an overflow conduit 61 to the well or open top vessel 59.

When the vacuum pump just described is not operating, the mercury column in U-tube 8| maintains the pressure diflerential between atmosphere, which is the pressure in vessel 55, and the vacuum in vessel 62 to which the absorber I4 is connected. Similarly, when the vacuum pump is not operating, the mercury column in fall tube 54 and vessel 65 maintains the pressure difierential between atmosphere, which is the pressure in conduit 66, and the vacuum in vessel 62 and absorber M. The quantity of mercury retained in vessel 85 must be such that there will be a sufficient amount to fill the fall tube 84 and still cover adequately the lower end of the fall tube.' It is desirable to make the fall tube 64 as long as possible, and this tube must be as long as the barometric height.

When the vacuum pump is operating, the difference in liquid levels in the two legs of U-tube 6| will correspond to the difierence in pressure maintained by the aspirator in vessel '55 and the pressure in vessel 62 in the high vacuum side. The mercury in conduit 61 is of a height equal to the vacuum pulled by the aspirator which is indicated in the drawing as hi. It will be noted that the U-tube 6| is also of barometric height hr with an additional length added thereto indicated at ha. The additional or extra length indicated as hz is added to the height of the U-tube 6! to insure a seal under all operating conditions encountered. For example, when the aspirator is shut oil, surging occurs in the U-tube 6| due to the momentum of the mercury flowing from vessel 55 to vessel 62.

If the fall tube 64 extended from the vessel 62 into the well 55 and the vessel 65 and conduit connection 66 were omitted, a single stage pump would be provided with gas trapped in vessel 52 passing through tube 64 and rising from the lower end thereof directly to the atmosphere in well 59. However, by providing a fall tube 84 of the character shown and employing an additional vessel 65 to which the conduit 66 is connected at one end with the other end connected to the aspirator, a vacuum pump is provided which is essentially a two stage pump. The first pressure stage is from the high vacuum side with which vessel 62 is associated to the pressure maintained in conduit 6G by the aspirator plus the head of the liquid column in vessel 65 which lsindicated as ha. The second pressure stage is from the aspirator pressure to atmospheric pressure.

By providing a two stage pump of the character described, the pressure is reduced evenly on both legs of the U-tube ii when the operation of the vacuum pump is first started and the pressure in as pointed out above. In a vacuum pump of this type circulation of mercury could only be started with much diiiiculty. In such case the fall tube 64 would necessarily extend into the well 59 a greater distance than the pump tubes 58 and the volume of vessel 55 must be sufiiciently large to vessel 62 is relatively high and near atmospheric pressure, for example. This is due to the fact that the pressure in the left-hand leg of U-tube I is reduced by the action of the aspirator, and the pressure in the right-hand leg of U-tube ll is also reduced by providing the conduit connection 66 so that the upper part of vessel 65 is subjected to the action of the aspirator. The lowering of the pressure in both legs of the U-tube BI is even when the operation of the vacuum pump is first started, except forthe constant pressure diiIerence of the liquid column in vessel 65, which,

is indicated in the drawing as ha. Compensation is made for the constant pressure diflerence h:

hold all of the mercury that would be pumped or raised from the well 59 through the tubes 58 to uncover the lower ends of the pump tubes 58. When operation of the aspirator is started and the pressure in vessel 55 is reduced, the fact that the conduit connection 66 is omitted would not permit an even pressure drop on both legs of the U-tube GI and the mercury may tend to move upward in the left-hand leg of U-tube 6|, especially when the pressure in vessel 62 is high and near atmospheric pressure. For this reason the. aspirator action is such that a suflicient amount of mercury would have to be raised through the riser tubes 58 to uncover the lower ends thereof and allow air to pass through the tubes 58 to build up the pressure in vessel 55. so that flow of mercury therefrom into vessel 62 would be effected. As soon as suflicient mercury returns to the well 59 through the fall tube B l, which has been assumed in the foregoing description to be of sufiicient length to extend into the well 59, the lower ends of the riser tubes 58 would again be covered and the cycle of operation just described would be repeated. These cycles would operation to occur, in the manner described above in connection with theembodiment of the invention illustrated.

In view of the foregoing, it will be apparent that in a two-stage vacuum pump of the character provided the starting operation is facilitated considerably, due to the manner in which the pressure drops on both legs of the U-tube 66. It has been observed that moisture in the mercury has no noticeable efiect on the operation of the vacuum pump.

-While a single embodiment of the invention has been shown and described, it will be apparent to those skilled in the art that various modifications and changes may be made without departing from the spirit and scope of the invention, as pointed out in the following claims.

What is claimed is:

1. An absorption refrigeration system having a generator and a condenser adapted to operate at one pressure and an evaporator and absorber adapted to operateat a lower pressure, and connections between the aforementioned parts to from said trap segregating gas passing into said conduit during the periods when gas can flow through said trap, the gas segregated between the successive bodies of liquid being carried by the latter through said conduit from the said one part to said other part.-

2. An absorption refrigeration system having a generator and a condenser adapted to operate at one pressure and an evaporator and absorber adapted to operate at a lower pressure, and connections between the aforementioned parts to provide circuits for circulation of refrigerant and absorption liquid, the circuit for circulation of refrigerant including a U-tube having a downleg connected to the condenser and an up-leg connected to the evaporator, the liquid in said U-tube serving to maintain the pressure diner-1 ential between the condenser and the evaporator, and a siphon trap arranged in the down-leg of said U-tube so that successive bodies-of liquid form in said trap and intermittently flow therefrom to trap gas in said down-leg which'passes therein during theperiods when flow of the gas can take place from the condenser through said trap.

3. Structure for removing non-condensible gas from a refrigeration system operating at low pressures including an open well adapted to contain mercury, a first vessel at a higher level than said well, a riser tube having the lower end thereof extending below the liquid level of mercury in said well and the upper end thereof extending into said first vessel, .vacuu'm producing means connected to said first vessel operative to reduce the pressure therein, the lower part of said riser tube having an air inletiopening wherebythe mercury in the lower part of the tube is broken into drops and raised through the tube to said first vessel due to the reduced pressure in the latter, a second vessel connected to a part of the refrigeration system, a U-tube having one leg connected to the lower part of said first vessel and the other leg connected to said second vessel,

whereby mercury flows through said U-tube from said first vessel to said second vessel, afall tube depending downward from said second vessel, the mercury entering said second vessel forming slugs and trapping gas at the upper part of 'said fall tube, a third vessel adapted to hold mercury and into which the lower end of the fall tube projects below the liquid level therein, a

conduit'for flowing mercury from said third vessel to said well, and a conduit connecting the upper-part of said third vessel .to said vacuum producing'means whereby the vapor space above the mercury in said third vessel is also at a reformed at the upper end of said "fall tube,

vacuum producing means, said'circuit being so formed and arranged that circulation of mercury therein is effected by said vacuum producing means, a vessel containing-mercury and into which the lower end of said fall tube extends,

- and said circuit including a connection whereby the pressure above the mercury in said vessel is reduced by said vacuum producingmeans.

--5. Structure for removing non-condensible gas from a refrigeration system having a plurality of parts and operable below atmospheric pressure, said structure including a fall tube pump having the upper end in communication with a part of said system, a U"-tube having one le thereof connected to the upper end of said fall tube pump, means including said U -tube for supplying liquid to said fall tube pump for downward flow therethrough, and a vacuum producing device connected tothe other leg of said U-tube and to the lower end of-said fall tube pump.

Pm P. ANDERSON, JR. 

